1. Field of the Invention
The present invention relates to an optical fiber, and more particularly to a multimode optical fiber having a graded refractive index profile.
2. Description of the Related Art
Conventional optical fibers include a core and a clad surrounding the core. The core has a relatively higher refractive index, and the core has a relatively lower refractive index. Optical fibers are classified into single mode optical fibers (SMFs) and multimode optical fibers (MMFs) according to the number of optical signal modes used therein. A core provided in a graded-index optical fiber (GRIN optical fiber) of multimode optical fibers has a graded refractive index profile.
Attenuation and bandwidth characteristics are important factors that determine the performance of the multimode optical fiber. It is known that a refractive index profile of the GRIN optical fiber can improve a transmission characteristic by minimizing differential mode delay (DMD) between modes within the optical fiber. Most conventional GRIN optical fibers have been employed in communication based upon light emitting diodes (LEDs).
FIG. 1 is diagram illustrating a method for launching light into a graded-index optical fiber. As shown in FIG. 1, a graded-index optical fiber 100 includes a core 110 and a clad 120. The method for launching light into the graded-index optical fiber 100 varies according to the light source being used. When the light source uses an LED, light is irradiated on an entire section of the core 110. However, when the light source uses a laser diode (LD), light is irradiated at the center of a section of the core 110.
Conventionally, the bandwidth of graded-index optical fibers have been measured using LEDs. However, since LDs are usually used for a high-speed communication network such as Gigabit Ethernet, the graded-index optical fiber's bandwidth can also be measured using the LD.
U.S. Pat. No. 6,438,303 entitled “LASER OPTIMIZED MULTIMODE FIBER AND METHOD FOR USE WITH LASER AND LED SOURCES AND SYSTEM EMPLOYING SAME” by John S. Abbott, III et al. states that it cannot meet the transmission characteristics required for a high transmission rate at both wavelengths 850 nm and 1300 nm for use in the graded-index optical fiber.
Since the required transmission capacity is high, a multimode optical fiber is necessary to support a transmission rate of one gigabit/second or more (e.g., 2.5 or 10-gigabit Ethernet) and satisfy the transmission characteristic required for a plurality of available wavelengths. However, in the prior art there is no appropriate method relating to the multimode optical fiber.